Columbian CO856 10x13-Inch Tyvek First Class Mail White Envelopes, 50 Count Designed for ultimate protection. Protect what's inside. Superior moisture, burst and tear resistant protection. Convenient and secure self-sealing Grip-Seal closure. Simply peel off release strip and press down for a quick, secure seal. First Class border ensures priority attention. Lightweight white Tyvek material. 10" x 13" 50 envelopes